I think the 4x4 and the Piggy Back 1 had similar drops. They had the rod attached to the auto advance rod. The problem with that set up is it would drop with out a case in the station. Kinda messy.
They changed that with the Piggy back two. ( not sure about the 4x4) They added a cam that is suppose to allow the activation rod to move to a slot when no case is present. Preventing a drop when no case is present.
I never liked ether one of those. Sooner or latter you will double clutch the handle when you get a primer hang up or a case not entering a die just right. Every time you move the handle it acting upon the powder drop.
You can work around it. But its a serious pain in the butt.
Case activated linkage and a powder check die is the only way to go.